A communication system provides for the communication of data between a sending station and a receiving station. The data is communicated between the sending and receiving stations by way of a communication channel that interconnects such stations. Data sourced at the sending station is converted into a form to permit its communication upon the communication channel. And, once delivered to the receiving station, recovery operations are performed upon the communicated data to recover the informational content thereof.
A radio communication system is an exemplary type of communication system. Communication channels defined in a radio communication system are defined upon radio links extending between the sending and receiving stations operable therein.
Because radio channels are utilized to communicate data between the sending and receiving stations, the need otherwise to install fixed, wireline connections to interconnect the sending and receiving stations, and to define communication channels thereon, is obviated. Therefore, infrastructure costs associated with the installation of a radio communication system are generally less than the corresponding infrastructure costs required to install the infrastructure of a wireline communication system. And, mobility can be provided to the communication stations operable in a radio communication system, thereby permitting mobile communications to be effectuated.
A cellular communication system is a type of radio communication system. Cellular communication systems have been installed throughout significant parts of the populated portions of the world. Cellular communication systems are constructed to be operable in compliance with operating specifications of any of various operating specifications.
A cellular communication system includes a network infrastructure that is installed throughout a geographical area that is to be encompassed by the communication system. The network infrastructure typically includes a plurality of fixed-site radio transceivers, referred to as base-transceiver stations, positioned at spaced-apart locations of the geographical area. Each of the base transceiver stations defines a region, referred to as a cell from which a cellular communication system derives its name.
Subscriber stations, usually referred to as mobile stations, positioned within the proximity of individual ones of the base transceiver stations are capable of communications therewith, thereby to permit effectuation of communication of data between the mobile station and a base transceiver station. Generally, a user of a mobile station is permitted access to the communication system to communicate there through the purchase of a service subscription for service in the communication system.
The radio communication channel defined upon the radio link extending between a mobile station and a base transceiver station usually exhibits non-ideal communication conditions. Radio communication channels defined in other types of radio communication systems, as well as communication channels defined in other types of communication systems, also usually exhibit non-ideal communication conditions. Data communicated upon such communication channels is distorted due to the non-ideal channel conditions. If the distortion is significant, the informational content of the communicated data cannot accurately be recovered at the receiving station.
A significant contribution to the distortion introduced upon the communicated data is due to fading conditions caused by multi-path transmission of the data. The fading might alter the values of information-bearing bits of the data during its communication upon the radio, or other, communication channel. Various techniques are utilized to compensate for the distortion introduced upon the data during its communication, thereby, to facilitate recovery of the informational content of the communicated data.
Generally, increase in the redundancy of the data that is communicated upon the communication channel increases the likelihood that the informational content of the data can be recovered, in spite of the fading exhibited upon the communication channel.
Encoding, techniques, for instance, are sometimes utilized to introduce time redundancy into the data. Introduction of time redundancy is sometimes referred to as creation of time diversity.
Spatial redundancy is sometimes also utilized. Spatial redundancy, sometimes referred to as space diversity, generally refers to the utilization of more than one transmit antenna transducer at a sending station from which to transmit data, upon separate physical paths, to the receiving station. Fading exhibited on one path might well not be exhibited on another path. And, a receiving station sometimes also utilizes more than one antenna transducer at which communicated data is detected and transduced into electrical form.
A communication system in which multiple transmit antennas and multiple receive antennas are utilized is sometimes referred to as a MIMO (multiple-input, multiple-output) communication system. In a MIMO communication system, independent data streams can be transmitted at different ones of the multiple transmit antennas. Communications in a MIMO system not only provide for improved communications upon non-ideal channels, but also permit the data throughput rate in such a communication system to be increased, generally corresponding to the increase in the number of transmit antennas. That is to say, the potential data throughput increase is linearly related with the number of transmit antennas systems that are utilized. And, to realize the potential data throughput increase permitted through the use of a MIMO system, the receiving station must also be able reliably to detect each of the individual data streams communicated by the sending station, in the presence of interference, that distorts the data caused by both inter-symbol interference (ISI) and interference caused by other data streams.
Optimally, the receiving station performs joint detection upon the multiple data streams. However, the complexity of equalization operations that are required to be performed pursuant to the joint detection increases exponentially, both with the number of transmit antennas and also with the length of the channel memory. The complexity of the equalization operations becomes so significant as generally to limit the practical utility of joint detection in many applications.
As recovery of the informational content of communicated data at a receiving station of a multiple-input, multiple-output communication system is facilitated through the use of joint detection utilizing joint equalization, any manner by which to facilitate joint equalization at a receiving station would be advantageous. And, more particularly, any manner by which to permit joint equalization operations to be performed at lessened levels of computational complexity would be advantageous.
It is in light of this background information related to communications in a MIMO communication system that the significant improvements of the present invention have evolved.